This invention relates to an optical disk drive.
An optical disk drive is so constituted as to write data on and/or read data from an optical disk by means of laser beam or the like. In the optical disk drive, an object optical system is carried on a linearly movable carriage that is movable along a surface of the optical disk.
Recently, an optical disk drive for double-sided optical disk has been developed. Such an optical disk drive has two movable carriages carrying objective lenses, which are linearly movable along the surfaces of the optical disk. Further, two separate optical units (such as laser source modules) are provided to stationary parts of the optical disk drive, each of which emits a beam to the respective carriage. However, because of the provision of two separate optical units, the structure of the optical disk drive may be complicated.
Thus, it is desired to provide a simple-structured optical device for a double-sided optical disk.
Further, a general optical disk drive (for a single-sided optical disk or a double-sided optical disk) is arranged to perform a xe2x80x98fine trackingxe2x80x99 using a so-called galvano mirror. The galvano mirror is rotated, thereby to change the incident angle of the beam on an objective lens, so that the beam spot minutely moves on the record surface of the optical disk.
FIGS. 1A and 1B schematically show the beam converged on a record surface 2a of an optical disk 2. When the incident angle of the beam on an objective lens 500 varies, the incident position of the beam on the objective lens 500 may also vary as shown in FIGS. 1A and 1B. In such a case, the incident beam is partially interfered with a surrounding member A (such as an aperture or the like) which surrounds the objective lens 500. This phenomena is called xe2x80x98wanexe2x80x99. When such wane occurs, the intensity of the beam on the record surface is lowered as shown in FIG. 2B. It may cause incorrect tracking operation.
Thus, it is desired to provide an optical disk drive capable of fine tracking without changing the incident position of the beam on the objective lens.
In order to increase the data storage capacity of the
It is therefore a first object of the present invention to provide a simple-structured optical device for a double-sided optical disk.
For the above object, according to one aspect of the present invention, there is provided an optical disk drive including two object optical systems, two carriage which carry the object optical systems and is movable along the surfaces of the optical disk, a separate optical unit (includes a laser source module) separated from the carriage, and a beam path selection system which selectively introduces the beam from the laser source to one of the object optical systems.
As constructed above, it is possible to selectively introduce the beam from the laser source module to one of the first and second carriages. Thus, one laser source module is commonly used for emitting beam to the first and second object optical systems. Accordingly, it is not necessary to provided two laser source modules, so that the structure of the optical disk drive is simplified.
In a particular arrangement, the beam path selecting system includes a movable mirror movable between first and second positions. Since the selecting of the beam path-selecting operation is performed by vertically moving the optical disk, it is necessary to increase NA (numerical aperture) of the objective lens, without increasing the size of the objective lens. For this purpose, a so-called near-field recording (NFR) technology is proposed. As shown in FIG. 3, the NFR technology has a hemisphere lens 510 provided between the objective lens 500 and the optical disk 2. The flat surface 511 of the hemisphere lens 510 is faced with the record surface 2a of the optical disk 2. A gap between the hemisphere lens 510 and the record surface 2a is less than 1 xcexcm. The beam that has passed through the objective lens 500 is converged on the flat surface 511 of the hemisphere lens 510. The converged beam is converted to a so-called xe2x80x98evanescent beamxe2x80x99 which propagates across the minute gap. Since the diameter of the evanescent beam is smaller than the converged beam, NA is remarkably increased. However, such NFR technology has a disadvantage that dust may easily be caught in the gap between the hemisphere lens 510 and the record surface 2a. Additionally, due to the use of the evanescent beam, the energy efficiency is relatively low, i.e., the intensity of the beam incident on the optical disk is relatively low.
Thus, it is desired to increase NA of an object optical system, without increasing the size of lenses and without using evanescent beam. movable mirror between two positions, the structure of the disk drive device is further simplified.
It is a second object of the present invention to enable a fine tracking operation without changing the incident of a beam on an object optical system.
For the above object, according to one aspect of the present invention, there is provided an optical disk drive including an object optical system which converges a beam on an optical disk, a movable carriage which carries the object optical system and is movable along the optical disk, a separate optical unit separated from the carriage. The separate optical unit includes a laser source module which emits a beam and a galvano mirror which is rotated thereby to change the incident direction of the beam on the object optical system. The optical disk drive device further includes a compensation system having a movable mirror provided in a beam path between the laser source module and the object optical system. The compensation system moves the movable mirror so that the beam from the laser source module is reflected by the galvano mirror and is incident on the object optical system substantially at the same position regardless of rotation amount of the galvano mirror.
As constructed above, the beam is incident on the object optical system substantially at the same position regardless of rotation amount of the galvano mirror. Thus, even when the galvano mirror rotates, the beam directing toward the object lens is not interfered with a surrounding member around the object optical system. That is, a xe2x80x98wanexe2x80x99 (as in FIG. 1B) does not occur. Therefore, the intensity of the beam on the optical disk is not lowered during the fine tracking operation. Accordingly, incorrect tracking operation is prevented.
Advantageously, the compensation system includes a distance detector which detects a distance between the galvano mirror and the object optical system. The amount (H) of movement of the movable mirror is determined based on a equation: H=L tan (2xcex8). L represents a distance between the galvano mirror and the object optical system. xcex8 represents a rotation angle of the galvano mirror.
It is a third object of the present invention to increase NA of an object optical system without increasing the size thereof and without using so-called evanescent beam.
For the above object, according to one aspect of the present invention, there is provided an optical disk drive including a laser source module which emits a beam, and an object optical system which converges the beam onto a optical disk. The optical disk includes a first lens, and a second lens that is substantially hemisphere-shaped (with a flat surface and a sphere surface). The second lens is located between the first lens and the optical disk so that a flat surface of the second lens is faced with the optical disk. A center of curvature of the sphere surface of the second lens is positioned between the first lens and a focal point of the first lens.
As constructed above, when the converging beam (directing toward the focal point) passes the sphere surface of the second lens, the beam refracts in a direction in which the beam further converges. Thus, NA is remarkably increased. Further, since evanescent beam (as in the NFR technology) is not used, the energy efficiency is high, i.e., the intensity of the beam is relatively high. Further, since the gap between the optical disk and the second lens is relatively large (compared with the NFR technology), dust may not easily be caught in the gap.
In a preferred embodiment, the optical disk drive further includes a movable carriage which carries the first lens and is movable along the optical disk, and a floating unit carrying the second lens. The floating unit is mounted to a resilient member extended from the movable carriage to the optical disk. The first lens is moved by a lens actuator (for example, a coil and a magnet) provided to the carriage. With this, the distance between the first lens and the optical disk can be xe2x80x98activelyxe2x80x99 controlled. The gap between the second lens and the optical disk is substantially kept constant by an air flow caused by the rotation of the optical disk.